I built Filestash (https://github.com/mickael-kerjean/filestash), an open source Dropbox like frontend for any cloud storage / protocols (S3, SFTP, FTP, SMB, NFS, etc...). This was made as a reflection of the Dropbox launch top comment with the infamous FTP guy as I was wondering what was missing from the FTP specs to be able to make a great interface to a protocol like FTP.

The money come from customisation and enterprise plugins (SSO, audit plugins, etc..). The entire product was made so you can quickly build custom file management solution by assembling a bunch of lego blocks (aka plugins)